Is there a connection among Hashimoto’s disease, hypothyroidism, and small intestinal bacterial overgrowth also known as SIBO? Does Hashimoto’s disease cause SIBO or does SIBO cause Hashimoto’s? I’ll answer these questions in my latest research review below.

There isn’t a lot of research, only two papers actually, on the specific connection between Hashimoto’s disease and SIBO which I’ll cover in this article. There are more papers on the connection between hypothyroidism and SIBO without mention of Hashimoto’s and the basic conclusion of those papers is that hypothyroidism is connected to SIBO because gastric motility is decreased in hypothyroidism. Decreased gastric motility basically means the food you eat is moving through the bowels to slowly so bacteria can build-up in the small intestine.

The first paper is entitled, “Association between Hypothyroidism and Small Intestinal Bacterial Overgrowth” published in the Journal of Clinical Endocrinology and Metabolism.

The authors begin by giving an overview of SIBO which is basically an overgrowth of bacteria in the small intestine which damages the gut wall leading to malabsorption of nutrients. The main signs and symptoms of SIBO are bloating, abdominal pain, cramping, gas, weight loss, and diarrhea or constipation or actually a mix of the two.

The main causes of SIBO are hypothyroidism, proton pump inhibitors and antacids, Helicobacter pylori, autoimmune disease, malnutrition, and immune dysfunction. Anything that can decrease gut motility may lead to SIBO such as gut surgeries, inflammation, metabolic issues, endocrine diseases, and muscle and nerve illnesses.

We know that thyroid hormones, especially T3, are involved with proper movement of food through the intestines known as peristalsis. Those with hyperthyroidism tend to have diarrhea and those with hypothyroidism tend to be constipated due to too much or too little thyroid hormone.

The authors wanted to answer three questions:

1. Is hypothyroidism associated with the development of SIBO?

2. How does treatment of SIBO affect those with hypothyroidism?

3. Does SIBO affect thyroid hormone levels?

How was this study on Hashimoto's Disease and SIBO done?

50 patients with hypothyroidism due to Hashimoto’s disease were enrolled. TSH, Free T4, Free T3, thyroid peroxidase (TPO), and antithyroglobulin antibody were tested. Hypothyroidism was considered a TSH above 2.8 and low Free T4 and Free T3 which was quite promising because most studies use a higher cut-off point for TSH. Thyroid antibody levels were elevated and thyroid ultrasounds were done showing tissue changes in the thyroid gland which is a normal sign in Hashimoto’s disease.

These patients were supplemented with synthetic T4 which normalized their thyroid function in 2-6 months before beginning the study. The good news is that we did have a control group of 40 healthy volunteers which strengthens the validity of the study.

A glucose breath test was done on everyone to measure hydrogen levels which is a gas produced by bacteria in the gut. Every patient who tested positive for SIBO was then treated with the antibiotic Rifaximin for 7 days. A glucose breath test was then repeated one month after the antibiotic tr...